oh im sorry I dint spot that part - it could still be mareks though, if it is very wobbly on its feet and unbalanced there is a good chance - try giving him plenty of mineral suppliments and check his vent - there may be a answer there. good luck :)
He may have mareks disease, i'm afraid it is fatal. it is common in silkies; I lost my silkie cockerel to it. it paralyses half of their body - wing and leg included, and prevents them from eating, drinking etc. we had to dispatch ourselves. it is unfortunately contagious, it trevls in feather...